The present invention relates to a photoelectric conversion element.
A photoelectric conversion element, which serves to convert a quantity of light into a quantity of electricity such as an electric charge quantity or change of conductance, is used in an image sensing device included in, for example, facsimile or a copying machines.
A photoelectric conversion element using a CCD (charge coupled device) is under development. However, the phosphor screen width is small in this element, with the result that it is necessary to reduce the optical information by a lens system for projection into the phosphor screen. Naturally, the photoelectric conversion element necessitates a reduction lens system, leading to enlargement of the device. Also miniaturization of the image is restricted by the reduction requirements.
A photoelectric conversion element which is substantially equal in width to the object is also under development. Naturally, a reduction lens system is unnecessary in this element. Such a conventional photoelectric conversion element is constructed as shown in FIGS. 1A and 1B, for example. FIG. 1A is a plan view showing a part of a photoelectric conversion element, and FIG. 1B is a cross-sectional view along line A--A shown in FIG. 1A. As seen from the drawing, a plurality of separate electrodes 2 made of aluminum or chromium are arranged in a row on a glass substrate 1. These separate electrodes 2 are covered with a photoelectric conversion layer 3. Further, the photoelectric layer 3 is covered with a transparent electrode 4. Since the transparent electrode 4 has low electric conductivity, an auxiliary electrode 5 is generally provided.
The overlapped portion of the separate electrodes 2, photoelectric conversion layer 3, and transparent electrode 4 performs the light detecting function. Thus, a photoelectric conversion element is designed such that the overlapped portion alone acts as a light sensing part. However, it is difficult to allow the transparent electrode 4 to overlap with the separate electrodes 2 only, i.e., not to allow the transparent electrode 4 to overlap with the lead-out parts 2a of the separate electrodes 2. In general, the transparent electrode 4 is formed by mask sputtering. There is about 200 .mu.m in repeatability error of mask alignment in the mask sputtering method. As a result, the transparent electrode 4 is partially overlapped with the lead-out parts 2a of the separate electrodes 2. Since the overlapped portion also detects light, noise is generated, resulting in deterioration of resolution in the sub-scanning direction.
Recently, an image sensing device has been demanded for reading out accurately fine images, which makes it desirable to finely divide the separate electrodes 2 to increase the density thereof. In the construction shown in FIGS. 1A and 1B, however, it is impossible to increase the separate electrode density satisfactorily because the signal lead-out parts 2a of the separate electrodes 2 are provided on one side only. The signal of the photoelectric conversion element is read out through lead wires connected to the signal lead-out parts 2a by using a wire bonder. In order to avoid mutual contact of adjacent lead wires, the maximum density of the signal read-out parts 2a in the post was 8 wires/mm. Naturally, the maximum density of the separate electrodes 2 was also 8 electrodes/mm, rendering it difficult to read out fine images of more than 8 lines/mm accurately.